Electromagnetic flux concentrator for levitation and heating



Nov. 21, 1967 J. REXER 3,354,285

ELECTROMAGNETIC FLUX CONCENTRATOR FOR LEVITATION AND HEATING Filed April 17, 1964 INVENTOR. JOACHIM REXER ATTORNEY levitation and heating of molten materials.

United States Patent Ofifice 3,354,285 ELECTROMAGNETIC FLUX CONCENTRATOR FOR LEVITATION AND HEATING Joachim Rexer, Parma, Ohio, assignor to Union Carbide Corporation, a corporation of New York Filed Apr. 17, 1964, Ser. No. 360,650 1 Claim. (Cl. 2197.5)

ABSTRACT OF THE DISCLOSURE Apparatus for the levitation and heating of materials comprising a source of alternating current connected to .a first circumferentially discontinuous annular body of electrically conductive material which is axially aligned with a second annular body of electrically conductive material arranged above .the first annular body and in flux linking relationship therewith.

The, present invention relates to apparatus for electromagnetic levitation and heating. More particularly, the present invention relates to an improved apparatus for concentrating electromagnetic flux whereby materials, both in the solid and molten state, can be conveniently levitated and heated.

-' The simultaneous suspension in space and heating of conducting materials by means of an electromagnetic field is known and apparatus are commercially available for this purpose.

- However, the presently known apparatus employ specially wound induction coils to provide the vertically .directed, diverging,

alternating current, and the eddy currents induced in the material create an electromagnetic field This electromagnetic field, which is opposite to the field of the levitating coil interacts therewith to provide a lifting force.

While the aforedescribed type of apparatus has been used with some degree of success, various disadvantages .are inherent which seriously limit itsapplication and effectiveness, particularly as regards the simultaneous For example, it is very difficult, if not practically impossible, to manufacturemulti-turn coils which have a sufliciently precise geometry so as to avoid asymmetrical distortions of the developed electromagnetic field which preclude stable levitation, particularly when the levitated material becomes molten.

Consequently, trial and error selection from a group of coils has been found to be necessary in order to find a coil having the least amount of distortion. Even when such a coil is found, it invariably requires the concurrent use of stabilizing coils which also must be selected, Moreover, when the most satisfactory coils have been selected and combined they must be used together and must be carefully handled and safeguarded from mechanical disturbances.

It is accordingly an object of the present invention to provide a simple and economical apparatus for stably levitating and heating electrically conductive materials.

It is another object to provide an apparatus which can be readily used to simultaneously levitate and heat electrically conductive materials both in the solid and molten state.

.strong easily machineable the angular member 3,354,285 Patented Nov. 21, 1967 Other objects will be apparent from the following description and claims, taken in conjunction with the drawing which shows in the several figures, various embodiments of the present invention.

Broadly, the apparatus of the present invention comprises an annular body formed of conductive material having a symmetrical inner surface which slopes inwardly and downwardly and serves as a concentrator for a levitating and heating electromagnetic field.

The present invention will be more clearly understood by reference to the drawing which shows in FIGURE 1 an annular electrically conductive member 1 which is preferably formed of copper although other materials such as silver and aluminum may be used. The annular member 1 is symmetrical and its inner surface 3 is machined to a downwardly and inwardly sloping conical surface as shown. Barrel member 5 surrounds annular member 1 and seals passage 7 therein which serves as a cooling passage for fluid e.g. water which is circulated through leads 2. The function of the closely coupled barrel member 5 in the present invention is to help ensure obtaining maximum energy transfer from all of the turns of the induction coil to the specimen located in the proximity of the opening in the annular member.

In the operation of the apparatus shown in FIGURE 1, coil 9 which surrounds at least a portion of annular member 1 and is in flux linking relation therewith is energized with alternating current to provide a vertically extending alternating electromagnetic field. Coil 9 does not require precision manufacture and can be of a standard type for example a cylindrically shaped coil of copper tubing.

Annular ring 1, which is in flux linking relation with coil 9 provides a symmetrical flux path which concentrates the electromagnetic field developed by coil 9 in a manner which provides a highly symmetrical levitation field. Annular member 1 is usually fabricated from a relatively material, such as copper which can be machined to provide a very high degree of symmetry and which has sufficient strength such that it is unaffected by routine use and handling. Such a device insures a concentrated flux path and the levitating field thus provides a uniform supporting medium.

In FIGURE 1 of the drawing, the inner surface 3 of 1 is a conical surface which has been found to be highly effective in providing stable levitation and heating of molten material. A curved inner surface 3', which can be a spherical surface, is also effective for the same purpose and is illustrated in FIGURE 2.

As shown in FIGURES 1 and 2, and also in the remaining figures of the drawing the annular flux concentrating members have a circumferential discontinuity, suitably in the form of a vertical slot 11; thereby preventing closed loop energy losses. That is to say, the discontinuity in the ring will prevent continuous circumferential current flow.

The embodiment of the present invention shown in FIGURES 3 and 4 illustrates the use of stabilizing members in the apparatus of the present invention.

When levitating and heating relatively large and dense solid materials, stabilizing means are not essential in the present invention however it generally is advantageous to use such devices particularly when levitating molten materials.

In FIGURE 3 the stabilizing means comprise reversed coil 13 and conductive annular member 15 which has a circumferential discontinuity 11' and an inner conical surface 8 sloping inwardly and upwardly i.e. opposite to the inner surface of flux concentrating means 1'.

Reversed coil 13 and coil 9' are connected together as shown and both coils are connected in circuit with alternating current source 17.

In operation, the material to be levitated and melted is placed on a support 19 which is adapted to be raised and lowered. The material thus arranged is located within the conical space defined by the flux concentrating annular member 1 and the coils are energized.

The field developed by coil 9' and concentrated by annular member 1 induces eddy currents in the material arranged on support 19 and as a result the material is levitated and heated. At the same time, an electromagnetic field is developed by reversed coil 13 and concentrated by annular member 15. This concentrated field is lesser and in opposite direction to the first field which is concentrated by annular member 1 and serves to provide lateral control for the levitated material and anchor it in the zone of high flux density.

A further embodiment of the present invention is shown in FIGURE 4 in which an annular member 21 having a symmetrical inner surface which extends inwardly and upwardly is employed as the stabilizing means. In this embodiment, the stabilizing annular member 21 is arranged in flux linking relation with the annular flux concentrating member 1 and no stabilizing coil is used, the opposing field of the stabilizing member being developed by eddy currents induced by the field of coil 9".

In an alternate modification, which is not illustrated in the drawing, a reversed coil connected in series with the levitating coil can be used as the sole stabilizing means being positioned in substantially the same location as the aforedescribed stabilizing means.

FIGURE of the drawing shows a still further embodiment of the present invention in which a source of alternating current is connected directly to annular flux concentrating member 1". In this embodiment no coils are used and the levitating and heating field is developed by the current flowing in the annular member itself which acts as a single turn coil.

A stabilizing annular member can be employed in the same manner, i.e. with direct electrical connections, which can be via the flux concentrating member, so that the current flow therein'is opposite to that in the flux concentrating member.

The following examples will serve to illustrate the present invention.

' EXAMPLE I An annular flux concentrating member of the type shown in FIGURE 1 was constructed of copper. The total height of the annular member was one inch and the outer diameter was 2% inches.

The upper inner diameter of the annular member was /1. inch and the lower inner diameter was /2 inch; the height of the conical surface thus defined was /2 inch and the apex angle of the conical surface was approximately 30 degrees.

The annular member was provided with a cooling passage of approximately /2" x 1 in cross-section through which water was circulated during operation.

The aforedescribed annular member was silver brazed to a barrel 6" in height whichwas formed of copper sheet. The arrangement of the barrel and annular flux concentrating member was as shown in FIGURE 1.

The levitator shown in FIGURE 1 was combined with stabilizing means as shown in FIGURE 3. A 17 turn coil of A" OD. copper tubing was arranged surrounding the levitator. Three opposed turns, in series connection with the coil surrounding the levitator, were arranged surrounding the stabilizer. A high frequency power source rate at 15 kw. output operating at an output of about amperes at 450 kc. was applied to the terminals of the coil and a /2" diameter sphere of aluminum was introduced into the conically shaped area defined by the annular flux concentrating means. The aluminum was levitated under these conditions and was melted and raised to a temperature of about 1000 C. The aluminum material was stably supported both in the solid and liquid condition. When molten the aluminum assumed a downwardly pointing conical shape.

EXAMPLE 11 Using the same equipment as in Example I a sphere of graphite /2 in diameter was stably levitated and heated to a surface temperature of 2800 0., measured by optical means.

What is claimed is:

An apparatus for the levitation and heating'of materials which comprises, in combination, (1) a source of alternating current (2) a first circumferentially discontinuous annular body formed of electrically conductive material being arranged with its central axis extending in a vertical direction, said annular body having an inner surface which is symmetrical about its vertical axis, said surface in downward extension converging at the vertical axis of said annular body and said annular body being connected to said source of alternating current to provide a flow of current through said annular body and the establishment of a vertically directed electromagnetic field (3) a second annular body formed of electrically conductive material being arranged above said first annular body in axial alignment and in flux linking relation therewith, said second annular body having an inner surface which is symmetrical about its vertical axis, said surface in upward extension converging at the vertical axis of said annular body. I

References Cited UNITED STATES PATENTS Kelly 21-9-10.51 X J. V. TRUHE, Primary Examiner. I 

